In a letter to his friend John Clellon Holmes in 1951, Jack Kerouac declared his intention to do to literature what he had done to the hardening conventions of postwar America: set it on fire, flying from spark to spark.

“The hell with these phony architectures,” Kerouac wrote to Holmes, and soon he rolled up teletype paper, sat down with notes from four years' worth of adventures, abandoned first drafts, employed a generous personal coffee maker and jammed out 186,000 continuous words on 120 yards of paper -- no paragraphs, no chapters. It was radical just to attempt such a feat, and though the work went through several edits and spent years on the shelf, its free-form, jazz-inspired core came to define a generation when finally published in 1957 as On the Road.

Incidentally -- despite even Kerouac’s own efforts -- its episodic, scattered nature also made it the antithesis of the three-act Hollywood film, making it seemingly impossible to adapt; just ask Francis Ford Coppola. Then, director Walter Salles and his longtime screenwriter Jose Rivera came along and found a way to wedge the most important beats of the book’s story into a digestible two-hour film.

“It’s as if the characters could be your friends. It’s as if, the distance between the writer and the character and the world you live in wasn’t unbridgeable,” Salles explained to The Hollywood Reporter last week. “And therefore, if you use a very free improvisational free-form, he’s also developing character and allowing you to understand, for instance, that the search for the missing father is the link between the two central characters. And at the same time, these young men who are searching for their fathers are also incapable of being fathers themselves. So there are light motifs that reverberate through the book -- in the 1957 version and in the scroll -- that allowed Jose to find an architecture that would do justice to the book and at the same time be filmable.”

In fact, this discovery came early in the writing process. Kerouac wrote On the Road as a fictionalized account of his adventures -- “a seamless blend of what has been lived and what has been imagined” -- through the truck beds, greasy diners, flophouses and jazz clubs of North America, at some point naming himself Sal Paradise and giving the name Dean Moriarty to his manic, catalyst friend Neal Cassady. In the finished book, he starts out by saying he first met Dean after splitting from his wife, but the original scroll marks the death of his father as the prominent recent life event.

“It’s been there since the Greeks: the search for the father, the difficulty of us being fathers, the desire to investigate the world in order to be able to write and be part of the creative process,” Salles said. “All of that -- again, since the Greeks -- those are themes that have never ceased to resonate because we have to confront them in order to truly find our place in the world.”

Salles’ agreement to take on the mammoth task of directing came with a pre-condition: that before shooting the film, he could travel around the country, in search of the monuments, highways, friends and intangible America that Kerouac described in his seminal novel. But in many ways, he already had taken that trip quite a few times, discovering new secrets each time he embarked.

“When I was 18 or 20, what I was mostly in love with was the fact that the book was an ode to freedom, all forms of freedom,” the Brazil-born director remembered. “The search that these characters were experiencing had to do with a desire to have an amplified perception of the world, leading to critical conscience. Later, I started to understand that this was one of the best narratives about the transition from youth to adulthood -- and all the moments of pain but also bliss that comes with it. And a little bit further, it also resonated because it’s a book about a writer trying to write a book. So it’s also an ode to literature, and to the creative process.”

Although it takes just a quick web search to find photos of Kerouac and Cassady, the pair -- and their fictional counterparts -- live more in the imaginations of the generations of people who have read On the Road, especially after both men died in the late 1960s. That gave Salles some leeway when it came to casting, though he first signed the film’s two most prominent women: Kirsten Dunst, who plays Dean’s wife Camille, and Kristen Stewart, who plays his young ex-wife/lover, Luanne. Cameos from Viggo Mortensen, Amy Adams, Elisabeth Moss and Steve Buscemi -- “I have a rule: it is not an indie film without Steve Buscemi,” Salles says -- highlight their different adventures.

Garrett Hedlund, reading his own beat poetry in the audition, made it easy to choose him for the frenetic, excitable and insatiable Dean. For Sal, the protagonist and narrator, Salles went for a bit of a wild card: Sam Riley, who played the tragic figure of Joy Division singer Ian Curtis, a terminally depressed young talent who hanged himself at age 23, in 2007’s Control.

“Sam allowed us to see so many layers of Ian Curtis, and I was very keen to see him read with us,” Salles explained. “And when those two acted together, something extremely resonant occurred. And they had the fire within that Garrett brought to Dean, and at the same time that intelligent sensibility of the writer that Sam was offering. It became the ideal match.”

Their energy is palpable, Riley following Hedlund’s lead as he pulls him from coast to coast in stolen cars filled with a rotating cast of women who have been just as charmed by Dean as Sal was. But, at least for Riley, the knowledge and perspective gained on the road, told in narration in the book, required a visual equivalent.

“The changes were mainly internal, and they were trying to reach new internal frontiers, and not only find the physical last American frontier,” the director explained. “So the camera had to be very close to the bodies and truly capture every single movement and every single moment of emotion that would be transmitted during the scenes.”

Indeed, whether during drugged freakouts or uncomfortable conversations in strange beds, each character has an intimate relationship with the audience. That personal connection, the feeling of admiration or even curiosity, works on the heart; Kerouac’s bigger message, which stands tall today just as it did a half-century ago, works on the brain.

“In many ways, the world that they were colliding against is still present today: There’s a wave of conservatism in not only America but in other parts of the world that is not dominant yet,” Salles warned. “In many parts of the world, there’s a very dangerous blend of politics and religion that defines what you can and can’t do, on so many levels. And this is getting closer and closer to becoming a real menace. And these characters in On the Road remind you there is something that is worth living beyond what is offered to you and that you should confront what you don’t agree with.”

The rebellion is personal, too; if not taking on the encroaching menace of church and state, simply rejecting a standard lifestyle is a kind of Kerouacian act.

"There was something in the culture of post-World War II society, and not only in America, that invited young men and women to play very specific roles in society and somehow feed the industrial process that was going to be amplified," the director said. "So going to live in the suburbs, having three children and a dog and a station wagon was exactly what the characters in On the Road didn’t want to do. The opposite: they were in search of their creative potential, they were trying to investigate all forms of forbidden territories. Sex and drugs were seen as ways to have a bigger vision of the world. So there was something in their actions that was revolutionary. But they didn’t know it at the time."